Cholestyramine pellets and methods for preparation thereof

ABSTRACT

The invention relates to small cholestyramine pellets that can be prepared by extrusion. The pellets have a high cholestyramine loading and are stable enough to be coated with one or more coating layers. The invention also relates to a process for the preparation of such pellets and to a multiparticulate drug delivery system comprising such pellets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No. 15/449,645, filed Mar. 3, 2017, which is a Continuation under 35 U.S.C. § 111(a) of International Application No. PCT/SE2017/050126, filed Feb. 9, 2017, which claims priority to SE 1650155-3, filed Feb. 9, 2016. The disclosure of the foregoing applications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to small cholestyramine pellets that can be prepared by extrusion. The pellets have a high cholestyramine loading and are stable enough to be coated with one or more coating layers. The invention also relates to a process for the preparation of such pellets and to a multiparticulate drug delivery system comprising such pellets.

BACKGROUND

Bile acid malabsorption is a condition characterized by an excess of bile acids in the colon, often leading to chronic diarrhea. Bile acids are steroid acids that are synthesized and conjugated in the liver. From the liver, they are excreted through the biliary tree into the small intestine where they participate in the solubilisation and absorption of dietary lipids and fat-soluble vitamins. When they reach the ileum, bile acids are reabsorbed into the portal circulation and returned to the liver. A small proportion of the secreted bile acids is not reabsorbed in the ileum and reaches the colon. Here, bacterial action results in deconjugation and dehydroxylation of the bile acids, producing the secondary bile acids deoxycholate and lithocholate.

In the colon, bile acids (in particular the dehydroxylated bile acids chenodeoxycholate and deoxycholate) stimulate the secretion of electrolytes and water. This increases the colonic motility and shortens the colonic transit time. If present in excess, bile acids produce diarrhea with other gastrointestinal symptoms such as bloating, urgency and fecal incontinence. There have been several recent advances in the understanding of this condition of bile salt or bile acid malabsorption, or BAM (Pattni and Walters, Br. Med. Bull. 2009, vol 92, p. 79-93; Islam and Di Baise, Pract. Gastroenterol. 2012, vol. 36(10), p. 32-44). Dependent on the cause of the failure of the distal ileum to absorb bile acids, bile acid malabsorption may be divided into Type 1, Type 2 and Type 3 BAM.

Diarrhea may also be the result of high concentrations of bile acid in the large intestine following treatment with drugs that increase the production of bile acids and/or influence the reabsorption of bile acids by the small intestine, such as treatment with ileal bile acid absorption (IBAT) inhibitors.

The current treatment of bile acid malabsorption aims at binding excess bile acids in the gastrointestinal tract, beginning in the proximal part of the small bowel, thereby reducing the secretory actions of the bile acids. For this purpose, cholestyramine is commonly used as a bile acid sequestrant. Cholestyramine (or colestyramine; CAS Number 11041-12-6) is a strongly basic anion-exchange resin that is practically insoluble in water and is not absorbed from the gastrointestinal tract. Instead, it absorbs and combines with the bile acids in the intestine to form an insoluble complex. The complex that is formed upon binding of the bile acids to the resin is excreted in the faeces. The resin thereby prevents the normal reabsorption of bile acids through the enterohepatic circulation, leading to an increased conversion of cholesterol to bile acids to replace those removed from reabsorption. This conversion lowers plasma cholesterol concentrations, mainly by lowering of the low-density lipoprotein (LDL)-cholesterol.

Cholestyramine is also used as hypolipidaemic agents in the treatment of hypercholesterolemia, type II hyperlipoproteinaemia and in type 2 diabetes mellitus. It is furthermore used for the relief of diarrhea associated with ileal resection, Crohn's disease, vagotomy, diabetic vagal neuropathy and radiation, as well as for the treatment of pruritus in patients with cholestasis.

In the current treatment of hyperlipidaemias and diarrhoea, the oral cholestyramine dose is 12 to 24 g daily, administered as a single dose or in up to 4 divided doses. In the treatment of pruritus, doses of 4 to 8 g are usually sufficient. Cholestyramine may be introduced gradually over 3 to 4 weeks to minimize the gastrointestinal effects. The most common side-effect is constipation, while other gastrointestinal side-effects are bloating, abdominal discomfort and pain, heartburn, flatulence and nausea/vomiting. There is an increased risk for gallstones due to increased cholesterol concentration in bile. High doses may cause steatorrhoea by interference with the gastrointestinal absorption of fats and concomitant decreased absorption of fat-soluble vitamins. Chronic administration may result in an increased bleeding tendency due to hypoprothrombinaemia associated with vitamin K deficiency or may lead to osteoporosis due to impaired calcium and vitamin D absorption. There are also occasional reports of skin rashes and pruritus of the tongue, skin and perianal region. Due to poor taste and texture and the various side effects, >50% of patients discontinue therapy within 12 months.

Another drawback with the current treatment using cholestyramine is that this agent reduces the absorption of other drugs administered concomitantly, such as oestrogens, thiazide diuretics, digoxin and related alkaloids, loperamide, phenylbutazone, barbiturates, thyroid hormones, warfarin and some antibiotics. It is therefore recommended that other drugs should be taken at least 1 hour before or 4 to 6 hours after the administration of cholestyramine. Dose adjustments of concomitantly taken drugs may still be necessary to perform.

In view of these side effects, it would be desirable if cholestyramine could be formulated as a colon release formulation, i.e. for release of the cholestyramine in the proximal part of the colon. Such a formulation may require a lower dose of cholestyramine and should have better properties regarding texture and taste, and may therefore be better tolerated by the patients. More importantly, colonic release of cholestyramine should be devoid of producing interactions with other drugs and should not induce risks for malabsorption of fat and fat-soluble vitamins, while still binding bile acids in order to reduce the increased colonic secretion and motility. For reasons of patient compliance, it would furthermore be desirable if the number of pills to be taken could be kept as low as possible. Each pill should therefore contain as much cholestyramine as possible.

EP 1273307 discloses preparations for preventing bile acid diarrhoea, comprising a bile acid adsorbent coated with a polymer so as to allow the release of the bile acid adsorbent around an area from the lower part of the small intestine to the cecum. It is shown that cholestyramine granules coated with HPMCAS-HF or ethyl cellulose displayed extensive swelling and bursting under conditions simulating the gastric environment.

Jacobsen et al. (Br. Med. J. 1985, vol. 290, p. 1315-1318) describe a study wherein patients who had undergone ileal resection were administered 500 mg cholestyramine tablets coated with cellulose acetate phthalate (12 tablets daily). In five of the 14 patients in this study, the tablets did not disintegrate in the desired place.

Despite progress made in this area, there still is a need for further improved cholestyramine formulations. In particular, there is a need for small cholestyramine particles that have a high cholestyramine content and are stable during the coating process.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that small and stable cores of cholestyramine can be obtained by extruding pellets of a mixture comprising cholestyramine and a vinylpyrrolidone-based polymer or a combination of a vinylpyrrolidone-based polymer and an acrylate polymer. Such pellets have a high cholestyramine content and are stable enough to withstand the conditions conventionally used for applying one or more coating layers onto the cores.

In a first aspect, the invention relates to pellets comprising at least 70% w/w cholestyramine and

-   -   i. at least 7% w/w of a vinylpyrrolidone-based polymer; or     -   ii. a combination of at least 6% w/w of a vinylpyrrolidone-based         polymer and at least 2% w/w of an acrylate copolymer; or     -   iii. a combination of at least 5% w/w of a         vinylpyrrolidone-based polymer and at least 3% w/w of an         acrylate copolymer; or     -   iv. a combination of at least 6% w/w of a vinylpyrrolidone-based         polymer, at least 1% w/w of an acrylate copolymer and at least         10% w/w microcrystalline cellulose; or     -   v. a combination of at least 5% w/w of a vinylpyrrolidone-based         polymer, at least 2% w/w of an acrylate copolymer and at least         20% w/w microcrystalline cellulose.

As used herein, the term “pellets” refers to extruded pellets, i.e. pellets obtained through extrusion and spheronization. The preparation of extruded pellets typically comprises the steps of mixing a powder with a liquid to obtain a wet mass, extruding the wet mass, spheronizing the extrudate and drying of the wet pellets.

It is essential that the pellets are stable enough to withstand mechanical stress during handling, such as during drying and coating of the pellets. The stability of the pellets may be expressed in terms of friability, which is the ability of a solid substance (such as a tablet, granule, sphere or pellet) to be reduced to smaller pieces, e.g. by abrasion, breakage or deformation. A low degree of friability means that the solid substance breaks into smaller pieces only to a low extent. As used herein, friability is defined as the reduction in the mass of the pellets occurring when the pellets are subjected to mechanical strain, such as tumbling, vibration, fluidization, etc. Methods for measuring friability are known in the art (e.g., European Pharmacopoeia 8.0, tests 2.9.7 or 2.9.41).

Experiments have shown that the inclusion of smaller amounts of vinylpyrrolidone-based polymer and/or acrylate copolymer than specified above results in lower yield and higher friability of the pellets. Although it is not possible to define acceptable friability limits for pellets in general, friability values of <1.7% w/w friability have been reported as acceptable to withstand stresses associated with fluid bed coating, handling and other processes (Vertommen and Kinget, Drug Dev. Ind. Pharm. 1997, vol. 23, p. 39-46). For the cholestyramine pellets of the present invention, it has been found that a friability of 2.1% is still acceptable. The friability is preferably lower than 2.0%, more preferably lower than 1.5%, and even more preferably lower than 1.0%.

The vinylpyrrolidone-based polymer may be polyvinylpyrrolidone (povidone) or a vinylpyrrolidone-vinyl acetate copolymer (copovidone). Povidone is a linear, water-soluble polymer made from N-vinylpyrrolidone. Copovidone (also known as copolyvidone) is a linear, water-soluble copolymer of 1-vinyl-2-pyrrolidone (povidone) and vinyl acetate in a ratio of 6:4 by mass. In a preferred embodiment, the vinylpyrrolidone-based polymer is copovidone.

The acrylate copolymer may be any pharmaceutically acceptable copolymer comprising acrylate monomers. Examples of acrylate monomers include, but are not limited to, acrylate (acrylic acid), methyl acrylate, ethyl acrylate, methacrylic acid (methacrylate), methyl methacrylate, butyl methacrylate, trimethylammonioethyl methacrylate and dimethylaminoethyl methacrylate. Several acrylate copolymers are known under the trade name Eudragit®.

Poly(ethyl acrylate-co-methyl methacrylate-co-trimethylammonioethyl methacrylate chloride) is a copolymer of ethyl acrylate, methyl methacrylate and a low content of trimethylammonioethyl methacrylate chloride (a methacrylic acid ester with quaternary ammonium groups). The copolymer is also referred to as ammonio methacrylate copolymer. It is insoluble but the presence of the ammonium salts groups makes the copolymer permeable. The copolymer is available as a 1:2:0.2 mixture (Type A) or as a 1:2:0.1 mixture (Type B). 30% aqueous dispersions of Type A and Type B are sold under the trade names Eudragit® RL 30 D and Eudragit® RS 30 D, respectively.

Poly(methyl acrylate-co-methyl methacrylate-co-methacrylic acid) 7:3:1 is a copolymer of methyl acrylate, methyl methacrylate and methacrylic acid. It is insoluble in acidic media but dissolves by salt formation above pH 7.0. A 30% aqueous dispersion is sold under the trade name Eudragit® FS 30 D.

Poly(methacrylic acid-co-ethyl acrylate) 1:1 is a copolymer of ethyl acrylate and methacrylic acid. It is insoluble in acidic media below a pH of 5.5 but dissolves above this pH by salt formation. A 30% aqueous dispersion is sold under the trade name Eudragit® L 30 D-55.

Further suitable acrylate copolymers include poly(ethyl acrylate-co-methyl methacrylate) 2:1, which is a water-insoluble copolymer of ethyl acrylate and methyl methacrylate. 30% aqueous dispersions are sold under the trade names Eudragit® NE 30 D and Eudragit® NM 30 D.

Preferred acrylate copolymers are ammonio methacrylate copolymer, poly(methyl acrylate-co-methyl methacrylate-co-methacrylic acid) 7:3:1, and poly(methacrylic acid-co-ethyl acrylate) 1:1. More preferably, the acrylate polymer is ammonio methacrylate copolymer, and most preferably the acrylate polymer is poly(ethyl acrylate-co-methyl methacrylate-co-trimethylammonioethyl methacrylate chloride) 1:2:0.2.

In one embodiment, the invention relates to pellets comprising at least 70% w/w cholestyramine and

-   -   i. at least 7% w/w of a vinylpyrrolidone-based polymer; or     -   ii. a combination of at least 6% w/w of a vinylpyrrolidone-based         polymer and at least 2% w/w of an acrylate copolymer.

In a more preferred embodiment, the invention relates to pellets comprising at least 70% w/w cholestyramine and

-   -   iii. at least 7% w/w copovidone; or     -   iv. a combination of at least 6% w/w copovidone and at least 2%         w/w ammonio methacrylate copolymer.

The pellets may further comprise an excipient such as microcrystalline cellulose. Microcrystalline cellulose, or MCC, is a purified, partly depolymerised cellulose with shorter, crystalline polymer chains. Its binding performance makes MCC one of the most commonly used fillers and binders in drug formulations.

In one embodiment, the pellets comprise from 0 to 20% w/w microcrystalline cellulose, such as from 0 to 10% w/w microcrystalline cellulose. In a more preferred embodiment, the pellets comprise from 0 to 5% w/w microcrystalline cellulose.

In another embodiment, the pellets are free from microcrystalline cellulose.

If the cholestyramine pellets are to be used for binding excess bile acids in the colon, they should be formulated for colon targeted delivery. This can be achieved by coating the cholestyramine pellets with one or more layers that delay the availability of the cholestyramine to the intestinal content until the pellets have reached the colon. The coated pellets may then be orally administered, e.g. in the form of a capsule wherein the coated pellets are contained, or as a sprinkle formulation that can be dispersed in liquid or soft food. For reasons of patient compliance, it is desirable that the total volume of the formulation is kept as low as possible. The cholestyramine content of the pellets should for that reason be as high as possible. The pellets of the invention contain at least 70% w/w cholestyramine, more preferably at least 75% w/w cholestyramine, more preferably at least 80% w/w cholestyramine, even more preferably at least 85% w/w cholestyramine and most preferably at least 90% w/w cholestyramine.

In one embodiment, the pellets comprise from 70 to 92% w/w cholestyramine, from 6 to 12% w/w of a vinylpyrrolidone-based polymer, from 2 to 5% w/w of an acrylate copolymer and from 0 to 20% w/w microcrystalline cellulose. More preferably, the pellets comprise from 80 to 92% w/w cholestyramine, from 6 to 12% w/w of a vinylpyrrolidone-based polymer, from 2 to 5% w/w of an acrylate copolymer and from 0 to 5% w/w microcrystalline cellulose.

In another embodiment, the pellets comprise from 70 to 92% w/w cholestyramine, from 6 to 12% w/w copovidone, from 2 to 5% w/w ammonio methacrylate copolymer and from 0 to 20% w/w microcrystalline cellulose. More preferably, the pellets comprise from 80 to 92% w/w cholestyramine, from 6 to 12% w/w copovidone, from 2 to 5% w/w ammonio methacrylate copolymer and from 0 to 5% w/w microcrystalline cellulose.

In another embodiment, the pellets comprise from 70 to 93% w/w cholestyramine, from 7 to 12% w/w of a vinylpyrrolidone-based polymer and from 0 to 20% w/w microcrystalline cellulose. More preferably, the pellets comprise from 70 to 93% w/w cholestyramine, from 7 to 12% w/w copovidone and from 0 to 20% w/w microcrystalline cellulose.

In yet another embodiment, the pellets comprise from 80 to 93% w/w cholestyramine, from 7 to 12% w/w of a vinylpyrrolidone-based polymer and from 0 to 10% w/w microcrystalline cellulose. More preferably, the pellets comprise from 80 to 93% w/w cholestyramine, from 7 to 12% w/w copovidone and from 0 to 10% w/w microcrystalline cellulose.

The size of the pellets is initially governed by the diameter of the screen used in the extrusion step. After the extrusion and spheronization steps, the pellets may be sieved to obtain a pellet fraction with a narrow size distribution. The diameter of the cholestyramine pellets is preferably from 500 μm to 3000 μm, more preferably from 750 μm to 2000 μm and even more preferably from 1000 to 1600 μm. In a most preferred embodiment, the diameter of the pellets is from 1000 to 1400 μm.

In another aspect, the invention relates to a process for the preparation of pellets comprising at least 70% w/w cholestyramine as disclosed herein, comprising the steps of:

-   -   i) mixing the dry ingredients;     -   ii) adding water, and optionally the acrylate copolymer, to         obtain a wet mass;     -   iii) extruding the wet mass;     -   iv) spheronizing the extrudate; and     -   v) drying the obtained pellets.

The dried pellets may thereafter be sieved in order to obtain pellets of uniform size.

The dry ingredients in step i) comprise cholestyramine and the vinylpyrrolidone-based polymer, and may optionally comprise an additional excipient, such as microcrystalline cellulose.

In a preferred embodiment, the invention relates to a process for the preparation of pellets comprising at least 70% w/w cholestyramine as disclosed herein, comprising the steps of:

-   -   i) mixing dry cholestyramine and copovidone, and optionally         microcrystalline cellulose;     -   ii) adding water, and optionally ammonio methacrylate copolymer,         to obtain a wet mass;     -   iii) extruding the wet mass;     -   iv) spheronizing the extrudate; and     -   v) drying the obtained pellets.

Because of its physical nature, cholestyramine powder is able to absorb large amounts of water, which results in considerable swelling of the material. In order to prepare a wet mass from dry cholestyramine, it is therefore necessary to add more water than normally would be used for preparing a wet mass from dry ingredients. Preferably, water is added to the mix of dry ingredients in an amount of at least 1.5 times the amount of cholestyramine (w/w), more preferably in an amount of at least 1.75 times the amount of cholestyramine (w/w), and even more preferably in an amount of at least 2 times the amount of cholestyramine (w/w).

The uncoated pellets rapidly disintegrate under aqueous conditions. However, they are stable enough to withstand the conditions necessary for applying a coating layer onto the pellets.

The cholestyramine pellets disclosed herein may be formulated for colon targeted delivery. They are then coated with one or more layers that delay the availability of the cholestyramine to the intestinal content until the pellets have reached the desired part of the colon. Techniques based on changes in the bacterial environment (i.e., enzyme controlled release) or pH (pH controlled release), based on gradual erosion of the coating (time controlled release) or based on diffusion through a permeable film (diffusion controlled release), or a combination of two or more of the above techniques may be used for controlling the release position and the rate of release of the pellets.

For enzyme controlled release, the pellets may be coated with polymers that are degraded by bacteria present in the colon, such as certain azo polymers and polysaccharides. Examples of bacterially degradable polysaccharides include chitosan, pectin, guar gum, dextran, inulin, starch and amylose, as well as derivatives thereof (Sinha and Kumria, Eur. J. Pharm. Sci. 2003, vol. 18, p. 3-18).

For pH controlled release, the pellets may be coated with a pH-sensitive polymer. Such polymers are typically insoluble below, but soluble above a certain pH value. The coating will therefore disappear from the pellets once the coated pellets reach an area of the gastrointestinal tract having a pH at which the polymer becomes soluble. Examples of such pH-sensitive polymers include, but are not limited to, cellulose acetate succinate, cellulose acetate phthalate, hydroxypropyl methylcellulose acetate succinate, hydroxypropyl methylcellulose phthalate, poly(methacrylic acid-co-methyl methacrylate) 1:1, poly(methacrylic acid-co-methyl methacrylate) 1:2, poly(methacrylic acid-co-ethyl acrylate) 1:1, poly(methyl acrylate-co-methyl methacrylate-co-methacrylic acid) 7:3:1, polyvinyl acetate phthalate, shellac, sodium alginate, and zein, as well as mixtures thereof.

For diffusion controlled release, the pellets may be coated with a polymer that is not water soluble at any pH, but that is permeable to water and small molecules dissolved therein. Examples of such polymers include, but are not limited to, ethyl cellulose (e.g., Surelease®); poly(vinyl acetate) (e.g., Kollicoat® SR 30 D); copolymers of ethyl acrylate, methyl methacrylate and aminoalkylmethacrylic acid ester such as poly(ethyl acrylate-co-methyl methacrylate-co-trimethylammonioethyl methacrylate chloride) 1:2:0.2 (Eudragit® RL 30 D) and poly(ethyl acrylate-co-methyl methacrylate-co-trimethylammonioethyl methacrylate chloride) 1:2:0.1 (Eudragit® RS 30 D); and copolymers of ethyl acrylate and methyl methacrylate, such as poly(ethyl acrylate-co-methyl methacrylate) 2:1 (Eudragit® NE 30 D or Eudragit® NM 30 D).

In order to improve the adherence of the coating layer onto the cholestyramine pellets, or in order to minimize the interaction between the coating layers and the cholestyramine in the pellets, an additional barrier coating may optionally be present between the pellet and the coating layer. A barrier coating may also be present when two different coating layers should be kept physically separated from each other. A particularly suitable material for the barrier coating is hydroxypropyl methylcellulose (HPMC).

The controlled release coating(s) and the optional barrier coating may comprise one or more additives, such as acids and bases, plasticizers, glidants, and surfactants. Examples of suitable acids include organic acids such as citric acid, acetic acid, trifluoroacetic acid, propionic acid, succinic acid, glycolic acid, lactic acid, malic acid, tartaric acid, ascorbic acid, pamoic acid, maleic acid, hydroxymaleic acid, phenylacetic acid, glutamic acid, benzoic acid, salicylic acid, mesylic acid, esylic acid, besylic acid, sulfanilic acid, 2-acetoxybenzoic acid, fumaric acid, toluenesulfonic acid, methanesulfonic acid, ethane disulfonic acid and oxalic acid, and inorganic acids such as hydrochloric acid, hydrobromic acid, sulphuric acid, sulfamic acid, phosphoric acid and nitric acid. Examples of suitable bases include inorganic bases such as sodium bicarbonate, sodium hydroxide and ammonium hydroxide. Examples of suitable plasticizers include triethyl citrate, glyceryl triacetate, tributyl citrate, diethyl phthalate, acetyl tributyl citrate, dibutyl phthalate and dibutyl sebacate. Examples of suitable glidants include talc, glyceryl monostearate, oleic acid, medium chain triglycerides and colloidal silicon dioxide. Examples of suitable surfactants include sodium dodecyl sulfate, polysorbate 80 and sorbitan monooleate.

The coatings may be applied onto the cholestyramine cores by methods known in the art, such as by film coating involving perforated pans and fluidized beds.

In another aspect, the invention relates to a multiparticulate drug delivery system comprising a plurality of coated cholestyramine pellets. In a preferred embodiment, the cholestyramine pellets are formulated for colon targeted delivery. In such an embodiment, the pellets are coated with one or more layers that delay release of the cholestyramine pellet until the coated pellet has reached the colon. In one embodiment, the colon targeted delivery is based on an enzyme-controlled release of the pellet. In another embodiment, the colon targeted delivery is based on a pH- and diffusion-controlled release of the pellet.

Because of its very low solubility, cholestyramine is not “released” from a formulation comprising coated cholestyramine pellets in that it dissolves from the formulation and diffuses into the intestine. Instead, the cholestyramine probably stays within the gradually degrading structure of the coated pellet. Therefore, as used herein, the term “release” of the cholestyramine refers to the availability of the cholestyramine to the intestinal content in order to bind components (i.e., bile acids) therein.

The low solubility of cholestyramine in aqueous environment prevents the release of cholestyramine from a formulation comprising coated cholestyramine pellets to be measured directly. The availability of the cholestyramine to the intestinal content over time and at different pH values may instead be determined in vitro, such as by measuring the sequestering capacity of the formulation under simulated conditions for the gastrointestinal tract. Such a method involves measuring the decreasing amount of free bile acid (i.e., the compound to be sequestered) in a liquid medium representative of the gastrointestinal tract. See also the Official Monograph for cholestyramine resin (USP 40, page 3404).

The invention is further illustrated by means of the following examples, which do not limit the invention in any respect. All cited documents and references are incorporated herein by reference.

EXAMPLES Example 1 Extrusion Experiments

All experiments were performed on a 100-200 g scale. The dry ingredients (cholestyramine, the vinylpyrrolidone-based polymer and/or microcrystalline cellulose) were mixed in the amounts indicated below. Water was added in portions of 50-100 gram with 3 minutes of mixing between each addition. When an acrylate copolymer was included in the experiment, it was added as a 2% w/w dispersion in water (20 g acrylate copolymer (aqueous dispersion 30%) added up to 300 g water). A final portion of pure water was added, if necessary. In each experiment, the total amount of liquid added was between 1.7 and 2.3 times the amount of solid material (w/w).

The wet mass was transferred to an extruder equipped with a 1.5 mm screen, operated at 25 rpm (revolutions per minute) and the extrudate was collected on a stainless steel tray. Approximately 100 g of the extrudate was run in the spheronizer for 1 minute at a speed of 730 rpm. The spheronized material was then transferred to stainless steel trays, placed in a drying oven and dried for 16 hours at 50° C. The yield was calculated as the fraction of pellets that pass through a 1.6 mm sieve but are retained on a 1.0 mm sieve.

Friability testing was performed using the equipment and procedure described in European Pharmacopoeia 8.0, test 2.9.7. The pellets were sieved on a 500 μm sieve to remove any loose dust before weighing.

The results using copovidone and Eudragit® RL 30 D are shown in Table 1, and the results using povidone and other Eudragit® copolymers are shown in Table 2.

TABLE 1 Amount (% w/w) Chole- Copo- Eudragit ® Yield Friability Entry styramine vidone MCC RL 30 D (%) (%) 1 100 0 0 0 * * 2 90 0 10 0 * * 3 70 0 30 0 39 1.6 4 70 6 24 0 * * 5 70 0 26 4 * * 6 70 6 20 4 85 0.1 7 80 3 15 2 * * 8 85 7.5 4.5 3 92 0.6 9 90 6 4 0 * * 10 90 0 6 4 * * 11 90 0 0 10 * * 12 90 6 0 4 85 1.4 13 90 10 0 0 87 1.2 14 91 9 0 0 82 0.5 15 92 8 0 0 83 1.5 16 93 7 0 0 78 1.0 17 94 6 0 0 * * 18 91 6 0 3 84 0.3 19 92 6 0 2 82 1.6 20 93 6 0 1 * * 21 85 6 8 1 81 3.5 22 80 6 13 1 85 0.8 23 92 5 0 3 70 2.0 24 93 5 0 2 * * 25 85 5 8 2 54 7.1 26 80 5 13 2 73 9.1 * = extrusion followed by spheronization did not lead to pellets.

TABLE 2 Amount (% w/w) Chole- Povi- Yield Friability Entry styramine done MCC Eudragit ® (%) (%) 1 85 7.5 4.5 3% w/w FS 30 D 79 0.2 2 85 7.5 4.5 3% w/w L 30 D-55 24 0.8 3 85 7.5 4.5 3% w/w NE 30 D 88 0.5 4 85 7.5 4.5 3% w/w NM 30 D 96 0.9 5 85 7.5 4.5 3% w/w RS 30 D 82 0.8

Example 2 Preparation of Pellets

Pellets with a composition according to Table 1, entry 8, were manufactured at a batch size of 200 g in the extrusion step and 100 g in the spheronization step. 170 g cholestyramine, 15 g copovidone and 9 g microcrystalline cellulose were charged into a planetary mixer. The mixer was operated at intermediate speed and the liquid was slowly added in portions with mixing between each addition. First 300 g water with 20 g Eudragit® RL 30 D (30% dry weight) was added in three equal portions, with mixing for 3 minutes between each addition. Finally 40 g pure water was added and mixing was performed for additionally 30 seconds. The wet mass was then transferred to the extruder. The extruder was equipped with a 1.5 mm screen, operated at 25 rpm and the extrudate was collected on a stainless steel tray. Approximately 100 g of the extrudate was run in the spheronizer for 1 minute at a speed of 730 rpm. The spheronized material was then transferred to stainless steel trays, placed in a drying oven and dried for 16 hours at 50° C. The dried pellets were sieved and the fraction between 1 mm and 1.6 mm was collected.

Example 3 Stability Testing of Cholestyramine Pellets

Pellets from example 1 (10 g) were added to 400 mL of a phosphate buffer (50 mM, pH 6.8) under stirring at 300 rpm using a propeller stirrer. The pellets of Table 1, entry 8 had fully disintegrated within 1 min 25 s, and the pellets of Table 2, entry 1 had fully disintegrated within 1 min 50 s. 

1. A population of pellets, each pellet comprising at least 70% w/w cholestyramine and an acrylate copolymer.
 2. The pellets of claim 1, wherein each pellet comprises at least 70% w/w cholestyramine.
 3. The pellets of claim 1, wherein each pellet comprises at least 75% w/w cholestyramine.
 4. The pellets of claim 1, wherein each pellet comprises at least 80% w/w cholestyramine.
 5. The pellets of claim 1, wherein each pellet comprises at least 85% w/w cholestyramine.
 6. The pellets of claim 1, wherein each pellet comprises at least 90% w/w cholestyramine.
 7. The pellets of claim 1, wherein each pellet comprises at least 1% w/w acrylate copolymer.
 8. The pellets of claim 1, wherein the acrylate copolymer is an ammonio methacrylate copolymer.
 9. The pellets of claim 1, wherein each pellet further comprises a vinylpyrrolidone-based polymer.
 10. The pellets of claim 9, wherein each pellet comprises at least 5% w/w vinylpyrrolidone-based polymer.
 11. The pellets of claim 9, wherein the vinylpyrrolidone-based polymer is copovidone.
 12. The pellets of claim 9, wherein each pellet further comprises microcrystalline cellulose.
 13. The pellets of claim 12, wherein each pellet comprises at least 10% w/w microcrystalline cellulose.
 14. The pellets of claim 1, wherein the pellets exhibit a friability of less than 2.1% as measured using the European Pharmacopoeia 8.0, test 2.9.7.
 15. The pellets of claim 14, wherein the pellets exhibit a friability of less than 2%.
 16. The pellets of claim 15, wherein the pellets exhibit a friability of less than 1.5%.
 17. The pellets of claim 16, wherein the pellets exhibit a friability of less than 1.0%. 